Low discrepancy and spectral gap for directed hypergraphs via spectral regularity lemma for tensors

We show that low discrepancy is equivalent to spectral gap for directed $k$-uniform hypergraphs. For undirected hypergraphs this recovers a theorem of Lenz and Mubayi, with a considerably shorter proof. At the heart of our argument is a Frieze--Kannan type spectral regularity lemma for hypergraphs b